A production method of the type described in the preamble is known from DE 4 334 203 C2. In said patent, there are embodiments with two dies to be introduced into the tube, said dies jointly filling the tube cross section. Using a plurality of dies is complex, both for tool production and for the production of the slots. Other embodiments in said document use only one die, which likewise fills the entire tube cross section, this being inherently more advantageous. For the production of the slots by means of a single die, provision is made for the die to be rotated through 180° from the working position into a retracted position after the formation of the slots, in order that the die can be removed from the tube again. However, realizing large rotational travels can have a negative impact on the cost-effectiveness of the manufacturing process, since longer cycle times may be necessary. In order to be able to realize adequately large collars on the slot edges, the die has axial connecting portions of relatively weak form between its axially arranged supporting portions (connecting portions—see FIG. 7, reference sign 4 in DE 4 334 203 C2). Cracks can therefore form in the die. Furthermore, only round tubes are shown in the publication. However, it is desirable to be able to provide tubes having as wide a variety of cross-sectional shapes as possible with slots.
U.S. Pat. No. 5,088,193 A also relates to the slotting of round tubes and the use of a single inner die. According to said publication, provision is made, firstly, for embossings to be formed in the tube wall with the aid of an arcuate punch corresponding to the contour of the tube. In the tube there is a die, the cross section of which is only slightly smaller than the inner tube cross section. Subsequently, the die is removed from the tube and the slots are produced with the aid of a piercing tool in the embossings created in the first step. A rotary movement of the die is not necessary here, since the latter is in the form of a continuous round bar, that is to say without supporting and connecting portions. There is nevertheless a disadvantage at least with regard to the cost-effectiveness of the manufacturing process.
In the production of slots, as described above, in principle no cuttings are produced as waste, this method differing from other known methods in which holes are cut out and the hole edges are bent in a flange-like manner.